The Quasiturbine or Qurbine engine is a pistonless rotary engine or pump using a substantially rhomboidal rotor which sides are hinged at the vertices. The volume enclosed between the sides of the rotor and the rotor housing provides compression and expansion in a fashion similar to Wankel engine, but the hinging at the edges allows the volume ratio to increase. The Quasiturbine is proposed as a Stirling engine, a pneumatic engine using stored compressed air, and as a steam engine.
Drawbacks with the Quasiturbine include the high amount of friction between the hinged vertices and sides of the rhomboidal rotor and the inner wall of the housing as well as the inner sides of the lateral covers, which results in energy loss as well as damage. Furthermore, the friction between the rhomboidal rotor of the Quasiturbine and the inner wall of the housing does not allow using this apparatus in the turbine mode with a gaseous fluid since the gas will escape between the pressurized compartments within the pump. As such, the Quasiturbine requires a starter.